Back to EveryPatent.com
United States Patent |
6,063,448
|
Duecoffre
,   et al.
|
May 16, 2000
|
Coating media, the use thereof, and a method of producing multilayer
coatings
Abstract
A coating medium suitable for multilayer coatings, containing, as a binder
vehicle:
______________________________________
A) 10 to 90% by weight
of one or more hydroxy-functional
(meth)acrylic copolymers, obtained from
a1) 20 to 40% by weight of hydroxyalkyl esters of (meth)acrylic acid
a2) 10 to 30% by weight of non-functionalised (meth)
acrylates
a3) 0 to 5% by weight of unsaturated carboyxlic acids
a4) 10 to 60% by weight of non-functionalised monomers
a5) 0 to 15% by weight of amino-functional monomers, and
a6) 0 to 5% by weight of multiply-unsaturated monomers
B) 90 to 10% by weight of hydroxy-functional polyesters,
C) 0 to 40% by weight of hydroxy-functional binder vehicles
D) 5 to 50% by weight of blocked polyisocyanates,
E) 5 to 40% by weight of components based on triazine which
crosslink with the hydroxyl groups of
components A), B) and C) with the
formation of ether and/or ester groups,
______________________________________
wherein at least 50% by weight of the (meth)acrylic copolymers, with
respect to the total amount of component A), has been produced in the
presence of the hydroxy-functional polyesters corresponding to at least
20% by weight of the total amount of component B).
Inventors:
|
Duecoffre; Volker (Wuppertal, DE);
Flosbach; Carmen (Wuppertal, DE);
Kerber; Hermann (Wuppertal, DE);
Schubert; Walter (Wuppertal, DE);
Herrmann; Friedrich (Wuppertal, DE);
Reifferscheid; Heinz-Walter (Bochum, DE);
Schild; Dirk (Wuppertal, DE)
|
Assignee:
|
Herberts GmbH (Wuppertal, DE)
|
Appl. No.:
|
981644 |
Filed:
|
March 9, 1998 |
PCT Filed:
|
July 4, 1996
|
PCT NO:
|
PCT/EP96/02944
|
371 Date:
|
March 9, 1998
|
102(e) Date:
|
March 9, 1998
|
PCT PUB.NO.:
|
WO97/03102 |
PCT PUB. Date:
|
January 30, 1997 |
Foreign Application Priority Data
| Jul 12, 1995[DE] | 195 25 375 |
Current U.S. Class: |
427/407.1; 427/409 |
Intern'l Class: |
B05D 007/14; B05D 003/02; B05D 001/36 |
Field of Search: |
427/409,407.1
|
References Cited
U.S. Patent Documents
3637546 | Jan., 1972 | Parker.
| |
4076766 | Feb., 1978 | Simms | 428/425.
|
4382114 | May., 1983 | Hohlein | 428/423.
|
4565730 | Jan., 1986 | Poth et al. | 428/204.
|
4960828 | Oct., 1990 | Higuchi et al. | 525/162.
|
5098956 | Mar., 1992 | Balsko et al. | 525/123.
|
5290633 | Mar., 1994 | Devlin et al. | 427/385.
|
5326820 | Jul., 1994 | Hoffmann | 525/123.
|
5336711 | Aug., 1994 | Schneider | 524/507.
|
5460892 | Oct., 1995 | Bederke | 428/482.
|
5466860 | Nov., 1995 | Flosbach | 560/43.
|
5698330 | Dec., 1997 | Bederke et al. | 427/409.
|
5731382 | Mar., 1998 | Bederke et al. | 427/409.
|
5739216 | Apr., 1998 | Duecoffre et al. | 528/438.
|
5753756 | May., 1998 | Aerts et al. | 525/111.
|
5759631 | Jun., 1998 | Rink et al. | 427/409.
|
5882734 | Mar., 1999 | Blum et al. | 427/407.
|
Foreign Patent Documents |
2 100 493 | Jan., 1994 | CA.
| |
0 036 975 | Oct., 1981 | EP.
| |
0 543 228 | May., 1993 | EP.
| |
0 604 922 | Jul., 1994 | EP.
| |
0653 468 A2 | Nov., 1994 | EP.
| |
42 23 182 | Jul., 1993 | DE.
| |
0 607 792 | Jul., 1994 | DE.
| |
WO 92/02590 | Feb., 1992 | WO.
| |
Primary Examiner: Dudash; Diana
Attorney, Agent or Firm: Pillsbury Madison & Sutro LLP
Claims
We claim:
1. A method of producing multilayer coatings comprising:
applying to a substrate a base lacquer coat comprising an aqueous coating
medium containing a pigment wherein said substrate is optionally
pre-coated,
overcoating said base lacquer coat with a transparent covering lacquer
coat;
wherein the transparent covering lacquer coat is produced from a
non-aqueous coating medium, containing as a binder vehicle:
______________________________________
A) 10 to 90% by weight
of one or more hydroxy-functional
(meth)acrylic copolymers, obtained from
a1) 20 to 40% by weight of one or more hydroxyalkyl esters of
(meth)acrylic acid
a2) 10 to 30% by weight of one or more non-functionalised (meth)
acrylates
a3) 0 to 5% by weight of one or more unsaturated carboyxlic acids
a4) 10 to 60% by weight of one or more non-functionalis
ed
monomers different from a2)
a5) 0 to 15% by weight of one or more amino-functional monomers
a6) 0 to 5% by weight of one or more multiply-unsaturat
ed
monomers
B) 90 to 10% by weight of one or more hydroxy-functional
polyesters,
C) 0 to 40% by weight of one or more hydroxy-functional binder
vehicles different from A) and B),
D) 5 to 50% by weight of one or more blocked polyisocyanates,
E) 5 to 40% by weight of one or more components based on
triazine which crosslink with the hydroxyl
groups of components A), B) and option-
ally C) with the formation of ether and/or
ester groups,
______________________________________
wherein the sum of components A) to E) adds up to 100% in each case, and
wherein at least 50% by weight of the (meth)acrylic copolymers, with
respect to the total amount of component A), has been produced in the
presence of one or more of the hydroxy-functional polyesters corresponding
to at least 20% by weight of the total amount of component B).
2. A method according to claim 1, wherein the non-aqueous coating medium
for producing the transparent covering lacquer coat contains as a binder
vehicle:
______________________________________
A) 10 to 90% by weight
of one or more hydroxy-functional
(meth)acrylic
copolymers, obtainable from
a1) 20 to 40% by weight of one or more hydroxyalkyl esters of
(meth)acrylic acid
a2) 10 to 30% by weight of one or more non-functionalised
(meth)acrylates
a3) 0 to 5% by weight of one or more unsaturated
carboxylic acids
a4) 10 to 60% by weight of one or more non-functionalised
monomers different
from a2)
a5) 0 to 15% by weight of one or more amino-functional monomers
a6) 0 to 5% by weight of one or more multiply-uns
aturated
monomers
B) 90 to 10% by weight of one or more hydroxy-functional
polyesters,
obtainable from
b1) 0 to 60% by weight of monocarboxylic acids of molecular
weight range 112 to 600
b2) 10 to 70% by weight of polycarboxylic acids of molecular weight
range 98 to 600 or
anhydrides of
polycarboxylic acids
of this type
b3) 5 to 40% by weight of tri- and/or polyhydric alcohols of
molecular weight range 100 to 400
b4) 0 to 40% by weight of dihydric alcohols of molecular weight
range 62 to 2000
b5) 0 to 30% by weight of monohydric alcohols of molecular
weight
range 100 to 400
b6) 0 to 15% by weight of hydroxycarboxylic
acids of molecular
weight range 90 to
280 or of lactones of
hydroxycarboxylic
acids of this type
b7) 0 to 15% by weight of aminoalcohols of molecular weight
range
61 to 300 and/or of
aminocarboxylic acids
of molecular weight
range 75 to 260
C) 0 to 40% by weight of one or more hydroxy-functional binder
vehicles different from A) and B),
D) 5 to 50% by weight of one or more blocked polyisocyanates,
E) 5 to 40% by weight of one or more components
based on
triazine which crosslink
with the hydroxyl
groups of components A),
B) and optionally
C) with the formation of
ether and/or ester
groups,
wherein the sum of components A) to E), a1) to a6) and b1) to b7) adds
up to 100% in each case,
and wherein at least 50% by weight of the (meth)acrylic copolymers, with
respect to the total amount of component A), has been produced in the
presence of one or more of the hydroxy-functional polyesters
corresponding to at least 20% by weight of the total amount of
component B).
______________________________________
3. A method according to claim 1, wherein the (meth)acrylic copolymers A)
have a number average molecular weight (Mn) of 1000 to 10000, an OH number
from 30 to 250 mg KOH/g and an acid number from 0 to 60 mg KOH/g and the
polyester resins B) have a number average molecular weight (Mn) of 200 to
5000, an OH number of 30 to 450 mg KOH/g and an acid number from 0 to 60
KOH/g.
4. A method according to claim 2, wherein the (meth)acrylic copolymers A)
have a number average molecular weight (Mn) of 1000 to 10000, an OH number
from 30 to 250 mg KOH/g and an acid number from 0 to 60 mg KOH/g and the
polyester resins B) have a number average molecular weight (Mn) of 200 to
5000, an OH number of 30 to 450 mg KOH/g and an acid number from 0 to 60
KOH/g.
5. A method according to claim 1, comprising:
applying the transparent covering lacquer coat wet-on-wet to the aqueous
base lacquer coat; and
stoving both layers jointly.
6. A method according to claim 2, comprising:
applying the transparent covering lacquer coat wet-on-wet to the aqueous
base lacquer coat; and
stoving both layers jointly.
7. A method according to claim 1, comprising:
applying the multi-layer coating during on-line lacquering of motor
vehicles.
8. A method according to claim 3, comprising:
applying the multi-layer coating during on-line lacquering of motor
vehicles.
Description
This application is the national phase of international application
PCT/EP96/02944 filed Jan. 30, 1997 which designated the U.S.
This invention relates to coating media which are particularly suitable for
multilayer stoving coatings for the series coating of automobiles, and
which are distinguished in particular by their high resistance to
chemicals, their high resistance to water of condensation and their
excellent condition for covering lacquer.
DE-A-43 38 703 describes a coating medium which contains a combination of
two different hydroxy-functional (meth)acrylic copolymers and which
contains a crosslinking agent combination comprising blocked
polyisocyanate and aminoplast resin. Polyester resin may optionally be
admixed with the (meth)acrylic copolymers as a further binder vehicle.
EP-A-0 541 604 and EP-A-0 206 072 describe acrylic polymers and the
production thereof. These acrylic polymers can be produced in the presence
of thinners, which may comprise polyester polyols. EP-A-0 036 975
describes clear lacquers for multilayer coatings, which consist of a
two-component system (2-C system) comprising a polyol component and a
polyisocyanate component which contains biuret and/or isocyanurate groups.
The polyol component is a polyester polyol which may be present in the
mixture with a polyacrylic resin. The polyacrylic resin can be produced in
the presence of the polyester polyol.
The object of the present invention was to provide coating media for
multilayer stoving coatings which are suitable for the series coating of
automobiles and which are distinguished by their high resistance to
chemicals, in particular acid resistance, their high resistance to water
of condensation and their excellent condition for covering lacquer.
It has been shown that this object can be achieved by a coating medium
which forms a subject of the present invention and which contains, as a
binder vehicle:
______________________________________
A) 10 to 90% by weight
of one or more hydroxy-functional
(meth)acrylic copolymers, obtained from
a1) 20 to 40% by weight of one or more hydroxyalkyl esters of
(meth)acrylic acid
a2) 10 to 30% by weight of one or more non-functionalised (meth)
acrylates
a3) 0 to 5% by weight of one or more unsaturated carboyxlic acids
a4) 10 to 60% by weight of one or more non-functionalis
ed
monomers different from a2)
a5) 0 to 15% by weight of one or more amino-functional monomers
a6) 0 to 5% by weight of one or more multiply-unsaturat
ed
monomers
B) 90 to 10% by weight of one or more hydroxy-functional
polyesters,
C) 0 to 40% by weight of one or more hydroxy-functional binder
vehicles different from A) and B),
D) 5 to 50% by weight of one or more blocked polyisocyanates,
E) 5 to 40% by weight of one or more components based on
triazine which crosslink with the hydroxyl
groups of components A), B) and option-
ally C) with the formation of ether and/or
ester groups,
______________________________________
wherein the sum of components A) to E) adds up to 100% in each case, and
wherein at least 50% by weight of the (meth)acrylic copolymers, with
respect to the total amount of component A), has been produced in the
presence of one or more of the hydroxy-functional polyesters corresponding
to at least 20% by weight of the total amount of component B).
The coating media according to the invention are formulated in particular
as single-component (1-C) systems.
According to a particularly preferred embodiment of the invention, the
hydroxy-functional polyesters of component B) of the binder vehicles are
obtainable from
______________________________________
b1) 0 to 60% by weight
of monocarboxylic acids of molecular weight
range 112 to 600
b2) 10 to 70% by weight of polycarboxylic acids
of molecular weight
range 98 to 600 or
anhydrides of poly-
carboxylic acids of
this type
b3) 5 to 40% by weight of tri- and/or polyhydric alcohols of
molecular weight range 100 to 400
b4) 0 to 40% by weight of dihydric alcohols of molecular weight
range 62 to 2000
b5) 0 to 30% by weight of monohydric alcohols of molecular weight
range 100 to 400
b6) 0 to 15% by weight of hydroxycarboxylic acids of molecular
weight range 90 to 280 or of
lactones of
hydroxycarboxylic acids of this type, and
b7) 0 to 15% by weight of amino alcohols of
molecular weight range
61 to 300 and/or of
aminocarboxylic acids of
molecular weight
range 75 to 260.
______________________________________
During the preparation of the binder vehicles contained in the coating
media according to the invention, at least 50% by weight, preferably more
than 70% by weight, of the total amount of (meth)acrylic copolymer A), and
most preferably the total amount thereof, is produced in the presence of
at least 20% by weight, preferably more than 30% by weight, most
preferably more than 40% by weight, of polyester resin B), wherein the
last-mentioned percentages by weight are quoted with respect to the total
amount of component B). If a plurality of polyesters is used as component
B), these may be present as a mixture during the production of
(meth)acrylic copolymer A), or individual polyesters or part of the
polyesters may be used and the remainder added at a later point in time.
Production of the (meth)acrylic copolymer A) may be effected by
radical-initiated polymerisation by the usual methods. In the course of
this procedure, at least 20% by weight, preferably more than 30% by
weight, most preferably more than 40% by weight, of polyester resin B) is
placed in the reaction vessel, preferably in admixture with suitable
organic solvents, and is heated to the reaction temperature, and at least
50% by weight, preferably more than 70% by weight, most preferably the
total amount of the monomer mixture, which optionally contains radical
initiators, for the synthesis of (meth)acylic copolymer A) is added. The
residual amount which may optionally remain of the monomer mixture, which
optionally contains radical initiators, for the synthesis of (meth)acrylic
copolymer A) may be polymerisaed by radical initiation in the same manner,
wherein organic solvent only, without proportions of polyester B), is
placed in the reaction vessel and is heated to the reaction temperature,
and the procedure thereafter is as described above. The (meth)acrylic
copolymer A) which is obtained by polymerisation of the residual amount of
monomer mixture which optionally remains can be admixed, during the
formulation of the coating medium according to the invention, with the
(meth)acrylic copolymer A) which was synthesised in the presence of
polyester resin B).
The expression "(meth)acrylic" which is used in the present description and
in the claims is synonymous with "acrylic" and/or "methacrylic".
The polymerisation is conducted, for example, at temperatures between
80.degree. C. and 180.degree. C., preferably at 100.degree. C. to
150.degree. C.
The polymerisation reaction can be started with known radical initiators.
Examples of radical initiators include dialkyl peroxides such as
di-tert.-butyl peroxide or di-cumyl peroxide; diacyl peroxides such as
dibenzoyl peroxide or dilauryl peroxide; hydroperoxides such as cumene
hydroperoxide or tert.-butyl hydroperoxide; peresters such as tert.-butyl
perbenzoate, tert.-butyl perpivalate, tert.-butyl
per-3,5,5-trimethylhexanoate or tert.-butyl per-2-ethylhexanoate;
peroxydicarbonates such as di-2-ethylhexyl peroxydicarbonate or
dicyclohexyl peroxydicarbonate; perketals such as
1,1-bis-(tert.-butylperoxy)-3,5,5-trimethylcyclohexane or
1,1-bis-(tert.-butylperoxy)-cyclohexane; ketone peroxides such as
cyclohexane peroxide or methyl isobutyl ketone peroxide; and azo compounds
such as 2,2'-azo-bis(2,4-dimethylvaleronitrile),
2,2'-azobis(2-methylbutyronitrile), 1,11-azobiscyclohexanecarbonitrile or
azobisisobutyronitrile; and C-C cleavage initiators such as such as
benzpinacol derivatives, for example.
The polymerisation initiators are. generally added, for example, in an
amount of 0.1 to 4% by weight, with respect to the amount of monomer
weighed in. The monomers may also be added separately or delayed
chronologicaly during the polymerisation. The monomers or the monomer
mixture used may contain the radical initiators or the radical initiators
may be added to the monomer mixture, optionally with a slight
chronological delay or separately.
Production of (meth)acrylic copolymer A) is effected, as described above,
in the presence of at least partial amounts of polyester resin B), which
is preferably provided dissolved in an organic solvent. Examples of
solvents which can be used include those which are also employed for the
polyester resin synthesis; the polyester resin may thus be provided as a
solution which was obtained during the production thereof. Other suitable
solvents may also be used, however. For example, customary lacquer
solvents are suitable, such as those which can be used later in the
coating media according to the invention, for example: glycol ethers such
as butyl glycol, butyl diglycol, dipropylene glycol dimethyl ether,
dipropylene glycol monomethyl ether or ethylene glycol dimethyl ether;
glycol ether esters such as ethyl glycol acetate, butyl glycol acetate,
3-methoxy-n-butyl acetate, butyl diglycol acetate or methoxypropyl
acetate; esters such as butyl acetate, isobutyl acetate or amyl acetate;
ketones such as methyl ethyl ketone, methyl isobutyl ketone, diisobutyl
ketone, cyclohexanone or isophorone; alcohols such as methanol, ethanol,
propanol or butanol; aromatic hydrocarbons such as xylene, Solvesso 100
(registered trade mark for a mixture of aromatic hydrocarbons with a
boiling range of 155 to 185.degree. C.) and aliphatic hydrocarbons may
also be used in a blend with the aforementioned solvents.
Chain transfer agents may be used in conjunction in order to regulate the
molecular weight. Examples include customary chain transfer agents, such
as mercaptans, thioglycolic acid esters, chlorinated hydrocarbons, cumene
and dimeric .alpha.-methylstyrene.
The polymerisation conditions (reaction temperature, period of admission of
the monomer mixture, solution concentration) are adjusted so that
(meth)acrylic copolymers A) for the coating medium produced according to
the invention have a number average molecular weight Mn (determined by gel
permeation chromatography using polystyrene as the calibration substanice)
between 1000 and 10,000.
The (meth)acrylic copolymers A), which contain hydroxyl groups, of the
coating medium produced according to the invention preferably have a glass
transition temperature range between -10 and +70.degree. C.
The (meth)acrylic copolymer A) preferably has an OH number of 30 to 250 mg
KOH/g and an acid number of 0 to 60, particularly 5 to 20 mg KOH/g.
Hydroxy-functionalised (meth)acrylates which contain primary and/or
secondary OH groups are used as component a1), for example, as monomers
for the production of hydroxy-functional (meth)acrylic copolymers A).
Examples of monomers having primary hydroxy functions include hydroxyalkyl
esters of .alpha.,.beta.-unsaturated carboxylic acids such as acrylic acid
and/or methacrylic acid having a primary OH group in the C.sub.2 -C.sub.3
hydroxyalkyl radical, such as hydroxyethyl (meth)acrylate, as well as
hydroxyalkyl esters of .alpha.,.beta.-unsaturated carboxylic acids, such
as acrylic acid and/or methacrylic acid, for example, having a primary OH
group in the C.sub.4 -C.sub.18 hydroxyalkyl radical, such as butanediol
monoacrylate, hydroxyethyl acrylate, hydroxyoctyl acrylate and the
corresponding methacrylates, for example, and reaction products of
hydroxyethyl (meth)acrylate with caprolactone.
Examples of monomers having secondary OH functions include hydroxypropyl
(meth)acrylate, addition products of glycidyl (meth)acrylate and saturated
short-chain fatty acids containing C.sub.2 -C.sub.3 alkyl radicals, e.g.
acetic acid or propionic acid, as well as addition products of glycidyl
esters of strongly branched monocarboxylic acids (the glycidyl ester of
versatic acid is obtainable under the trade name Cardura E) with
unsaturated COOH-functional compounds, such as acrylic and/or methacrylic
acid, maleic acid or crotonic acid for example, addition products of
Cardura E with unsaturated anhydrides such as maleic anhydride for
example, reaction products of glycidyl (meth)acrylate with saturated,
branched or unbranched fatty acids comprising C.sub.4 -C.sub.20 alkyl
radicals, e.g. butanoic acid, caproic acid, lauric acid, palmitic acid,
stearic acid or arachidic acid. The reaction of acrylic acid or
methacrylic acid with the glycidyl ester of a carboxylic acid comprising a
tertiary .alpha.-carbon atom may be effected before, during (in situ) or
after the polymerisation reaction, in the sense of a reaction analogous to
a polymerisation.
The preferred monomers a1) are 1,4-butanediol mono(meth)acrylate,
hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate.
Non-functionalised (meth)acrylates can be used as component a2) as monomers
for the production of the hydroxy-functional (meth)acrylic copolymer A),
for example, such as branched or unbranched saturated monomers such as
alkyl (meth)acrylates having C.sub.8 -C.sub.18 chains in the alkyl
component, e.g. ethylhexyl (meth)acrylate, octyl (meth)acrylate,
3,5,5-trimethylhexyl (meth)acrylate, decyl (meth)acrylate, dodecyl
(meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate,
cyclohexyl (meth)acrylate, lauryl acrylate-1214, isobornyl (meth)acrylate
or 4-tert.-butylcyclohexyl methacrylate. Further examples include short-
or medium chain, branched or unbranched saturated monomers, such as alkyl
(meth)acrylates having C.sub.1 -C.sub.7 chains in their alkyl component,
e.g. methyl (meth)acrylate, ethyl (meth)acrylate, propyl acrylate, butyl
(meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate,
tert.-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate,
cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl
(meth)acrylate, 3,5,5-trimethylhexyl (meth)acrylate, decyl (meth)acrylate,
dodecyl (meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate
and octadecenyl (meth)acrylate.
The preferred monomers a2) comprise butyl (meth)acrylate, ethylhexyl
(meth)acrylate, cyclohexyl (meth)acrylate and isobutyl (meth)acrylate.
Examples of suitable unsaturated carboxylic acids of component a3) include
unsaturated mono- and/or dicarboxylic acids and/or semi-esters of
dicarboxylic acids, such as acrylic, methacrylic, itaconic, crotonic,
isocrotonic, aconitic, maleic and fumaric acids for example, semi-esters
of maleic and fumaric acids, and .beta.-carboxyethyl acrylate and addition
compounds of hydroxyalkyl esters of acrylic acid and/or methacrylic acid
with carboxylic acid anydrides, such as phthalic acid
mono-2-methacryloyloxyethyl ester, and semi-esters of maleic anhydride
formed by the addition of saturated aliphatic alcohols, such as ethanol,
propanol, butanol and/or isobutanol, for example.
Acrylic acid is the preferred monomer a3).
Component a3) is preferably used in the production of the (meth)acrylic
copolymer in a proportion such that an acid number of 5 to 20 mg KOH/g of
the (meth)acrylic copolymer A) is obtained.
Monovinyl aromatic compounds are examples of monomers of component a4)
which are different from a2). These preferably contain 8 to 10 carbon
atoms per molecule. Examples of suitable compounds include styrene, vinyl
toluenes, .alpha.-mathylstyrene, chlorostyrenes, o-, m- or
p-methylstyrene, 2,5-dimethylstyrene, p-methoxystyrene,
p-tert.-butylstyrene, p-dimethylaminostyrene, p-acetamidostyrene and
m-vinylphenol, vinyl esters of alpha, alpha-dialkyl-substituted branched
aliphatic monocarboxylic acids (for example the commercial product VEOVA
10 of Shell AG), as well as alkyl esters of maleic, fumaric,
tetrahydrophthalic, crotonic, isocrotonic, vinylacetic and itaconic acid,
such as the corresponding methyl, ethyl, propyl, butyl, isopropyl,
isobutyl, pentyl, amyl, isoamyl, hexyl, cyclohexyl, 2-ethylhexyl, octyl,
3,5,5-trimethylhexyl, decyl, dodecyl, hexadecyl, octadecyl and octadecenyl
esters, and also gamma-methacryloxypropyl trimethoxysilane.
Styrene and derivatives thereof, such as vinyl toluenes, for example, are
preferably used as monomers of component a4).
Examples of monomers of component a5) include those comprising terminal
tertiary amino groups such as tert.-aminomethyl methacrylate or
tert.-aminopropyl methacrylate. When using monomers of this type, it is
advisable to avoid the simultaneous use of glycidyl-functionalised
monomers, since gelling of the polymer cannot otherwise be ruled out.
In addition, small proportions of monomers of component a6) which contain
at least two polymerisable, olefinically unsaturated double bonds may also
be used. The proportion of these monomers is preferably less than 5% by
weight with respect to the total weight of monomers. Examples of compounds
of this type include hexanediol diacrylate, hexanediol methacrylate,
ethylene glycol diacrylate, ethylene glycol dimethacrylate, butenediol
diacrylate, butanediol dimethacrylate, hexamethylene-bis-methacrylamide,
trimethylolpropane triacrylate, trimethylolpropane trimethacrylate and
similar compounds.
The polyester resins B) preferably have number average molecular weights of
200 to 5000, most preferably 1000 to 3000, an OH number of 30 to 450 mg
KOH/g, most preferably from 120 to 280 mg KOH/g, and an acid number of 0
to 60 mg KOH/g, most preferably from 2 to 35 mg KOH/g, and may be
produced, for example, by condensation polymerisation from components b1)
to b7). The condensation polymerisation may be effected by the usual
methods familiar to one skilled in the art, for example in the presence of
customary crosslinking catalysts and at elevated temperatures, e.g. from
180 to 250.degree. C., and in the melt for example. Entrainment agents,
such as xylene for example, may also optionally be used.
The percentages by weight of components b1) to b7) which are used in the
production of the polyester are selected in particular so that the desired
OH numbers are obtained.
Examples of suitable monocarboxylic acids b1) include benzoic acid,
tert.-butylbenzoic acid, hexahydrobenzoic acid, saturated fatty acids such
as 2-ethylhexanoic acid, isononanoic acid, coconut oil fatty acid,
hydrogenated industrial fatty acids or fatty acid mixtures for example,
decanoic acid, dodecanoic acid, tetradecanoic acid, stearic acid, palmitic
acid, docosanoic acid, unsaturated fatty acids, such as soyabean fatty
acid, sorbic acid, groundnut oil fatty acid, conjuene fatty acid, tall oil
fatty acid, safflower oil fatty acid and mixtures of these or other
monocarboxylic acids, for example. The proportion of monocarboxylic acids
is preferably more than 10% by weight and less than 40% by weight.
2-ethylhexanoic acid and isononanoic acids are preferably used as
monocarboxylic acid b1).
Component b2) is used in an amount of 10 to 70% by weight, for example from
10 to 40% by weight. Examples of suitable polycarboxylic acids b2) or
anhydrides include phthalic acid or anhydride, isophthalic acid,
terephthalic acid, tetrahydrophthalic acid or anhydride, hexahydrophthalic
acid or anhydride, 1,3- and 1,4-cyclohexanedicarboxylic acid, maleic acid
or anhydride, succinic acid or anhydride, fumaric acid, adipic acid,
sebacic acid, azelaic acid, dimeric fatty acids, trimeric fatty acids,
trimellitic acid or anhydride, pyromellitic acid or anhydride, and
mixtures of these or other acids.
The preferred polycarboxylic acids b2) are adipic acid and cycloaliphatic
dicarboxylic acids such as hexahydrophthalic acid or anhydride and
1,4-cyclohexanedicarboxylic acid.
Examples of suitable tri- and polyhydric alcohols b3) include glycerol,
trimethylolpropane, pentaerythritol, dipentaerythritol and mixtures of
these or other polyhydric alcohols.
The preferred tri- and polyhydric alcohols b3) are trimethylolpropane and
pentaerythritol.
Examples of suitable dihydric alcohols b4) include ethylene glycol, 1,2-
and 1,3-propylene glycol, 1,3-, 1,4- and 2,3-butanediol, 1,5-pentanediol,
1,6-hexanediol, 2,5-hexanediol, trimethylhexanediol, diethylene glycol,
triethylene glycol, hydrogenated bisphenols, 1,4-cyclohexanediol,
1,4-cyclohexanedimethanol, neopentyl glycol, tricyclodecanediol and
mixtures of these or other diols.
The preferred dihydric alcohols b4) are 1,6-hexanediol and neopentyl
glycol.
Examples of suitable monohydric alcohols b5) include n-hexanol,
cyclohexanol, decanol, dodecanol, tetradecanol, octanol, octadecanol,
natural and synthetic fatty alcohols, such as lauryl alcohol, Ocenol
110/130 (manufactured by Henkel) and mixtures of these and other alcohols,
for example.
Examples of suitable starting components b6) include dimethylolpropionic
acid, lactic acid, malic acid, tartaric acid, epsilon-hydroxycaproic acid,
ricinoleic acid or epsilon-caprolactone.
The preferred components b6) are dimethylolpropionic acid and
epsilon-caprolactone.
Examples of suitable starting components b7) include aminoethanol,
2-aminopropanol, diethanolamine, aminoacetic acid or 6-aminohexanoic acid.
Examples of suitable esterification catalysts for the production of the
polyester resin B) may comprise: dibutyltin oxide, sulphuric acid or
p-toluenesulphonic acid.
After the condensation polymerisation is complete, the solids content of
polyester resin B) may optionally be adjusted by dilution with suitable
organic solvents. Examples of suitable organic solvents include the
solvents mentioned above for the synthesis of the (meth)acrylic copolymer
A), or mixtures of these or other solvents.
The (meth)acrylic copolymer A) is produced, as described above, in the
presence of the polyester resin B).
The hydroxy- and optionally carboxy-functional (meth)acrylic copolymers A)
and polyester resins B) which can be used may be "chain-lengthened" with a
lactone. Lactones (cyclic ethers) add to hydroxyl and/or carboxyl groups,
whereupon the ring is opened and a new terminal hydroxyl or carboxyl group
is formed. Epsilon-caprolactone is an example of a particularly preferred
lactone.
Examples of other lactones include lactones such as beta-propiolactone,
delta-valerolactone, gamma-butyrolactone, zeta-enantholactone and
eta-caprylolactone. Lactones of this type may be substituted: examples
thereof include 6-methyl-epsilon-caprolactone,
3-methyl-epsilon-caprolactone, 5-methyl-epsilon-caprolactone,
5-vinyl-epsilon-caprolactone,4-methyl-delta-valerolactone,3,5-dimethyl-eps
ilon-caprolactoneand mixtures thereof. The reaction with the lactone may be
effected immediately following the resin synthesis, for example, namely
following the synthesis of the (meth)acrylic polymer A) and/or of the
polyester resin B). The reaction is conducted, for example, at elevated
temperature, e.g. at temperatures up to 100.degree. C. The reaction may be
carried out for up to 10 hours with stirring, for example.
The coating media according to the invention may contain, as component C),
one or more hydroxy-functional binder vehicles which are different from A)
and B), for example (meth)acrylic copolymer resins which are different
from A), or polyester resins or even polyurethane resins which are
different from B). The coating media according to the invention preferably
contain no further binder vehicles in addition to A) and B).
The coating media according to the invention contain one or more blocked
polyisocyanates as component D).
Examples of polyisocyanates which can be used in blocked form as component
D) in the coating medium according to the invention include
cycloaliphatic, aliphatic or aromatic polyisocyanates such as
1,2-propylene diisocyanate, 2,3-butylene diisocyanate, tetramethylene
diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethylene
diisocyanate, 1,12-dodecane diisocyanate, cyclohexane 1,3- and
1,4-diisocyanate,
1-isocyanato-3,3,5-trimethyl-5-isocyanato-methylcyclohexane (=isophorone
diisocyanate: IPDI), perhydro-2,4'- and/or 4,4'-diphenylmethane
diisocyanate, 1,3- and 1,4-phenylene diisocyanate, toluene 2,4- and
2,6-diisocyanate, diphenylmethane-2,4'- and/or-4,4'-diisocyanate, 3,2'-
and/or 3,4-diisocyanato-4-methyl-diphenylmethane, naphthylene
1,5-diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate,
triphenylmethane 4,4'-triisocyanate, tetramethylxylylene diisocyanate or
mixtures of these compounds.
In addition to these simple isocyanates, those which contain hetero atoms
in the radical linking the isocyanate groups are also suitable. Examples
of these include polyisocyanates containing carbodiimide groups,
allophanate groups, isocyanurate groups, uretdione groups, urethane
groups, acylated urea groups and biuret groups.
The known polyisocyanates which are primarily used for the production of
lacquers are particularly suitable for the invention, e.g. modification
products, which contain biuret, isocyanurate or urethane groups, of the
aforementioned simple polyisocyanates, particularly
tris-(6-isocyanatohexyl)-biuret, the isocyanurate derived from isophorone
diisocyanate or hexane diisocyanate, or polyisocyanates containing low
molecular weight urethane groups, such as those which can be obtained by
the reaction of isophorone diisocyanate, used in excess, with simple
polyhydric alcohols of molecular weight range 62 to 300, particularly with
trimethylolpropane. Any mixtures of the said polyisocyanates may also of
course be used for the production of the products according to the
invention.
Other suitable polyisocyanates include the known prepolymers containing
terminal isocyanate groups, which can be obtained in particular by the
reaction of the aforementioned simple polyisocyanates, primarily
diisocyanates, with less than stoichiometric amounts of organic compounds
containing at least two groups capable of reacting with isocyanate groups.
Compounds such as these which are preferably used are those which contain
a total of at least two amino groups and/or hydroxy groups and which have
a number average molecular weight of 300 to 10,000, preferably 400 to
6000. The corresponding polyhydroxyl compounds are preferably used, e.g.
the hydroxypolyesters, hydroxypolyethers and/or acrylate resins containing
hydroxyl groups which are known in the art in polyurethane chemistry. In
these known prepolymers, the ratio of isocyanate groups to hydrogen atoms
which are reactive towards isocyanate groups corresponds to 1.05 to 10:1,
preferably 1.1 to 3:1, wherein the hydrogen atoms preferably originate
from hydroxyl groups. Moreover, the type and quantitative ratios of the
starting materials used in the production of the NCO prepolymers are
preferably selected so that the NCO prepolymers have an average NCO
functionality of 2 to 4, preferably from 2 to 3, and a number average
molecular weight of 500 to 10,000, preferably from 800 to 4000.
It is also possible to use copolymers of the vinylically unsaturated
monoisocyanate dimethyl-m-isopropenylbenzyl isocyanate as a
polyisocyanate, as described, amongst other features, in DE-A-41 37 615.
Customary blocking agents may be used, such as customary CH-acid, NH-, SH-
or OH-functional compounds which facilitate crosslinking under hardening
conditions. Examples include CH-acid compounds such as acetylacetone or
CH-acid esters such as acetoacetic acid alkyl esters or malonic acid
dialkyl esters, aliphatic or cycloaliphatic alcohols such as n-butanol,
isopropanol, tert.-butanol, furfurol, 2-ethylhexanol, or cyclohexanol;
phenols such as cresol or tert.-butylphenol, dialkylaminoalcohols such as
dimethylaminoalcohol, oximes such as methyl ethyl ketoxime, acetone oxime,
cyclohexanone oxime or acetophenone oxime, lactams such as e-caprolactam
or pyrrolidone-2, imides such as phthalimide or N-hydroxy-maleic imide,
hydroxyalkyl esters, hydroxamic acids and esters thereof, N-alkylamides
such as methylacetamide, imidazoles such as 2-methylimidazole, or
pyrazoles such as 2,3-dimethylpyrazole. Mixtures of these blocking agents
may also be used, however.
Within the scope of the present invention, CH-acid esters and/or oximes are
preferred as blocking agents for the polyisocyanates. CH-acid esters are
particularly preferred. The alkyl groups of the esters, which in malonic
acid dialkyl esters or acetoacetic acid esters may be the same or
different, preferably contain 1 to 5 carbon atoms. Examples of malonic
acid dialkyl esters include C.sub.2 -C.sub.5 alkyl esters, such as malonic
acid dimethyl, diethyl, diisopropyl, dibutyl, di-tert. -butyl and dipentyl
esters. Malonic acid diethyl ester is particularly preferred. Examples of
acetoacetic acid alkyl esters include C.sub.2 -C.sub.5 alkyl esters, such
as acetoacetic acid methyl, ethyl, isopropyl, butyl, tert.-butyl and
pentyl esters. Acetoacetic acid ethyl ester is particularly preferred.
Examples of preferred oximes include acetone oxime and butanone oxime. It
is also possible to use mixtures of these blocking agents.
The molar ratio of the blocking agents, which contain active hydrogen, to
the NCO groups of the isocyanates, for example the ratio of the malonic
acid dialkyl esters and/or acetoacetic acid alkyl esters to NCO groups,
can be varied, for example from 0.5:1 to 1.5:1. When there is an excess of
NCO, the free NCO groups may optionally be reacted with other reactants.
The blocking reaction with CH-acid compounds may preferably be catalysed.
The catalysts used for the blocking of the polyisocyanates are preferably
alkali hydroxides, for example alkali metal hydroxides such as lithium,
sodium and/or potassium hydroxide. The anhydrous alkali metal hydroxides
are preferably used. Lithium hydroxide is most preferably used. The
catalysts are used in small amounts, for example in amounts of 0.1 to 2%
by weight, preferably 0.3 to 1% by weight, with respect to the weight of
isocyanate and CH-acid blocking agent. The catalysts are used in solid
form, e.g pulverised, and are removed from the reaction mixture after the
completion of the blocking reaction, by filtration for example.
More than one type of protective group, for example those of different
reactivities, may also be used for blocking.
It is thus possible, for example, to use a mixture of two or more different
blocked polyisocyanates D) or to use a polyisocyanate which is blocked
intramolecularly with two or more different protective groups.
In addition, the coating media according to the invention contain one or
more components E) based on triazine, which crosslink with the hydroxyl
groups of components A), B) and optionally C) with the formation of ether
and/or ester groups.
Preferred examples of the components E) based on triazine, which crosslink
with the hydroxyl groups of components A), B) and optionally C) with the
formation of ether and/or ester groups, include melamine resins which are
customary as crosslinking agents, such as methyl-etherified melamine
resins such as the commercial products Cymel 325, Cymel 327, Cymel 350 and
Cymel 370 or Maprenal MF 927, for example. Other examples of melamine
resins which can be used include butanol- or isobutanol-etherified
melamine resins such as the commercial products Setamin US 138 or Maprenal
MF 610, for example; mixed etherified melamine resins which are both
butanol- and methanol-etherified, such as Cymel 254, and also
hexamethyloxymethyl-melamine (HMMM), such as Cymel 301 or Cymel 303,
wherein the latter may require an external acid catalyst for crosslinking,
such as p-toluenesulphonic acid for example. Acid catalysts of this type
may optionally be blocked, ionically or non-ionically, with amines or
polyepoxides.
Components E) based on triazine, which crosslink with the hydroxyl groups
of components A), B) and optionally C) with the formation of ether and/or
ester groups are transesterification crosslinking agents, particularly
transesterification crosslinking agents which react with the hydroxyl
groups with the formation of urethane groups (carbamic acid ester groups),
such as preferably tris(alkoxycarbonylamino)triazine, for example, as
described in EP-A-0 604 922.
Apart from the aforementioned solvents, the coating media which contain the
binder vehicles to be used according to the invention may contain
customary lacquer auxiliary materials in addition, for example spreading
agents, e.g. those based on (meth)acrylic homopolymers, silicone oils,
plasticisers such as esters of phosphoric acid, phthalic acid or citric
acid, rheology influencers, such as pyrogenic silica or microgels,
urea-containing reaction products of primary amines and polyisocyanates
("sagging control agents"), hydrogenated castor oil, hardening
accelerators such as phosphoric acid, phosphoric acid esters, dicarboxylic
acid semi-esters, or citric acid, for example; organic metal salts such as
dibutyltin laurate, zinc naphthenate or bismuth tricarboxylate, and also
compounds which contain tertiary amino groups such as triethylamine, and
light stabilisers.
The coating media according to the invention may also exist in
water-thinnable form. If an aqueous emulsion is to be produced, the
solvent used for the production of the binder vehicle containing
components A) and B) is substantially removed. This may be effected by
distillation for example, optionally under vacuum. Provided that it
contains acidic groupings, the binder vehicle concentrate which is
obtained in this manner, which contains components A) and B) and which has
a high solids content of 90% by weight for example, can then be
neutralised with a customary base, e.g. ammonia or an organic amine, e.g
triethylamine. The neutralised binder vehicle containing A) and B) which
is obtained can be emulsified in water, optionally after the admixture of
crosslinking agents D) and E). This can be effected, for example, with
intensive stirring and with heating if necessary, for example to
temperatures of 30 to 80.degree. C., e.g. 50.degree. C.
It is also possible for monomers comprising basic groupings, e.g. those
which contain tertiary amine groups, to be polymerised in during the
production of the (meth)acrylic copolymer A). Monomers of component E) are
examples of monomers such as these. The binder vehicle containing basic
groups which is produced in this manner can then be neutralised with
acids, e.g. inorganic or organic acids such as formic acid or acetic acid.
The neutralised binder vehicle containing A) and B) can be emulsified in
water, optionally after the admixture of crosslinking agents D) and E).
This can be effected, for example, with intensive stirring and with
heating if necessary, for example to temperatures of 30 to 80.degree. C.,
e.g. 50.degree. C.
Alternatively, the binder vehicle containing A) and B) can be emulsified
with the aid of a non-ionic emulsifier. This is effected, for example, by
homogenisation of the binder vehicle concentrate, optionally together with
crosslinking agents D) and E) and one or more non-ionic emulsifiers, and
optionally with heating, for example to temperatures of 30 to 80.degree.
C., e.g. 60.degree. C. A mixture of this type can be homogenised in a
customary homogenisation device. Examples of the latter include
rotor/stator homogenisers which operate at speeds of 8000 to 10,000
revolutions per minute, for example. The emulsifiers are used in amounts
of 3 to 30% by weight, for example, with respect to the binder vehicle
concentrate. Water-insoluble components of the coating medium, e.g.
lacquer additives such as light stabilisers or spreading agents based on
silicone oils, for example, may be admixed with the binder vehicle
concentrate before conversion into the aqueous phase and emulsified
together with it.
The coating media according to the invention are particularly suitable for
the production of a transparent outer coat (clear lacquer coat) in the
production of oven-drying multilayer coatings. The outer coat may be
applied by the wet-into-wet process, for example, whereupon both coats are
hardened jointly. Therefore, the invention also relates to a method of
producing multilayer coatings and to the use of the coating media for the
production thereof. In this respect, the non-aqueous coating media which
are preferred according to the invention may be applied as transparent
covering lacquers to coats comprising aqueous or solvent-containing base
lacquers for hardenable multilayer coatings.
Pigmented coating media may also be produced. Customary organic and/or
inorganic colouring pigments and/or extenders may be used for this
purpose, such as titanium dioxide, micronised titanium dioxide, iron oxide
pigments, carbon black, silica, barium sulphate, micronised mica, french
chalk, azo pigments, phthalocyanine pigments, quinacridone or
pyrrolopyrrol pigments.
The coating media according to the invention are applied by known methods,
such as spraying, dipping, rolling or by doctor blade. In the course of
this procedure, the covering lacquer coating is applied to the substrate,
which is optionally already provided with further lacquer coats. The
coating media according to the invention can also be applied by a spraying
process using supercritical carbon dioxide as a solvent. The content of
organic solvents can thereby be considerably reduced. After a vapour
extraction phase, the applied coating medium is preferably crosslinked by
heating. The stoving temperatures are preferably between 80 and
160.degree. C., most preferably between 120 and 150.degree. C. The
hardening times are of the order of 20 to 40 minutes, for example. The
coat thickness of the stoved film is about 15 to 50 .mu.m, for example. A
hard, crosslinked glossy lacquer coating is thus obtained. One preferred
embodiment is the application of the coating medium according to the
invention as a clear lacquer coating on to a base lacquer. This may
preferably be effected wet-into-wet, or the base lacquer may be previously
dried by heating. A particularly good adhesion between the two coats is
obtained.
For example, base lacquers which may contain customary covering lacquer
pigments can be overcoated with coating media according to the invention
which are formulated as clear lacquers. The base lacquers preferably
contain effect pigments, such as metallic pigments for example. Polyester,
polyurethane or acrylate resins are preferably used as the binder vehicle
basis of the base lacquer. These binder vehicles may optionally be
crosslinked via crosslinking agents, e.g. melamine or isocyanate
derivatives.
The coating media according to the invention are particularly suitable for
covering lacquers or clear lacquers which are preferably used in the motor
vehicle industry but are also used in other fields. The use of the coating
medium according to the invention in multilayer coating is particularly
suitable for the series coating of automobiles.
The coating media according to the invention are particularly suitable for
producing a transparent outer coat of an oven-drying multilayer coating.
They are particularly suitable for the series coating of automobiles and
parts thereof.
The covering lacquer coats, e.g. clear lacquer coats, which are produced
using the coating media according to the invention, and which contain
(meth)acrylic copolymers A) synthesised in the presence of polyester
resins B), are distinguished by their superior resistance to chemicals,
particularly their resistance to acids, and by their excellent status as
covering lacquers, as well as by their resistance to water of condensation
(which is manifested in a particularly favourable humidity chamber
resistance).
EXAMPLE 1
393.1 g isononanoic acid, 1.4 g phosphoric acid (85%), 287.4 g
hexahydrophthalic anhydride, 274.9 g pentaerythritol and 43.2 g xylene
were introduced into a reaction apparatus suitable for the synthesis of a
polyester. The batch was heated to 210.degree. C. over 5 hours with water
being split off, with stirring and whilst passing inert gas over the
batch. After an acid number of about 23 was reached, the batch was cooled
to 140.degree. C. and was diluted to a solids content of 70% by weight
with SOLVESSO 100 (a commercial product manufactured by Shell AG).
EXAMPLE 2
170.3 g 1,6-hexanediol, 128.9 g trimethylolpropane, 0.9 g phosphoric acid
(85%), 37 g xylene, 228.2 g hexahydrophthalic anhydride and 278.6 g
dimeric fatty acid were introduced into a reaction apparatus suitable for
the synthesis of a polyester. The batch was heated to 220.degree. C. over
5 hours with water being split off, with stirring and whilst passing inert
gas over the batch. After an acid number of about 25 was reached, the
batch was cooled to 140.degree. C. and was diluted to a solids content of
80% by weight with SOLVESSO 100 (a commercial product manufactured by
Shell AG).
EXAMPLE 3
440 g of the polyester solution from Example 1, 28 g xylene, 73 g n-butyl
acetate and 90.7 g SOLVESSO 100 (a commercial product manufactured by
Shell AG) were placed in a 2 litre three-necked flask with ground glass
joints, which was fitted with a stirrer, a contact thermometer and a
dropping funnel, and were heated to 138.degree. C. with stirring and with
reflux cooling in operation. A mixture of 2.5 g acrylic acid, 49.5 g butyl
acrylate, 93 g 2-hydroxyethyl methacrylate, 154 g styrene, 2.2 g
di-tert.-butyl peroxide and 7 g tert.-butyl peroctoate were added
continuously over 6 hours. The batch was then polymerised for 4 hours at
138.degree. C., cooled to 100.degree. C., and diluted with 60.1 g n-butyl
acetate. The polymer solution had a solids content of 62.6%, an acid
number of 16.5 mg KOH/g, an OH number of 135 mg KOH/g and a viscosity of
1440 mPa.s/25.degree. C.
EXAMPLE 4
420 g of the polyester solution from Example 2, 30 g n-butanol and 140 g
SOLVESSO 100 (a commercial product manufactured by Shell AG) were placed
in a 2 litre three-necked flask with ground glass joints, which was fitted
with a stirrer, a contact thermometer and a dropping funnel, and were
heated to 147.degree. C. with stirring and with reflux cooling in
operation. A mixture of 3 g acrylic acid, 55 g butyl acrylate, 100 g
2-hydroxyethyl methacrylate, 167 g styrene and 9 g di-tert.-butyl peroxide
was added continuously over 4 hours. The batch was then polymerised for 4
hours at 145.degree. C., cooled to 100.degree. C., and diluted with 76 g
SOLVESSO 100. The polymer solution had a solids content of 67.0%, an acid
number of 14.0 mg KOH/g, an OH number of 144 mg KOH/g and a viscosity of
2460 mPa.s/25.degree. C.
EXAMPLE 5
A single-component clear lacquer was produced by homogeneously mixing 32.0
parts of the resin solution from Example 3 with 17.0 parts of the resin
solution from Example 1, 15.5 parts of a 65% solution of a malonic acid
diethyl ester-capped isocyanurate of isophorone diisocyanate in SOLVESSO
100, 16.3 parts of a 55% solution of a butanol-etherified melamine resin,
1.0 parts of a light stabiliser of the benzotriazole type, 0.5 parts of a
light stabiliser of the HALS type, 0.7 parts of a 10% silicone oil
solution, 5 parts of n-butanol and 12 parts of SOLVESSO 100 (a commercial
product manufactured by Shell AG).
EXAMPLE 6
A single-component clear lacquer was produced by homogeneously mixing 29.6
parts of the resin solution from Example 4 with 17.0 parts of the resin
solution from Example 1, 15.5 parts of a 65% solution of a malonic acid
diethyl ester-capped isocyanurate of isophorone diisocyanate in SOLVESSO
100, 16.3 parts of a 55% solution of a butanol-etherified melamine resin,
1.0 parts of a light stabiliser of the benzotriazole type, 0.5 parts of a
light stabiliser of the HALS type, 0.7 parts of a 10% silicone oil
solution, 5 parts of n-butanol and 14.4 parts of SOLVESSO 100 (a
commercial product manufactured by Shell AG).
Bodywork panels which had been previously coated with commercially
available cathodically depositable electro-dip lacquer (KTL) (18 .mu.m)
and commercially available primer surfacer, as used in the series coating
of automobiles, were coated with commercially available, water-thinnable
metallic base lacquer to a dry coat thickness of 15 .mu.m and pre-dried
for 6 minutes at 80.degree. C. Immediately thereafter, the clear lacquer
from Example 5, 6 or from a comparative example (Example 2 from EP-A-0 653
458) was applied wet-into-wet, by spray application, to give a dry coat
thickness of 35 .mu.m, and after vapour removal for 5 minutes at room
temperature was stoved for 20 minutes at 140.degree. C.
The results obtained are given in Table 1. The tests were performed
according to the general industry standards. The drop test with 10%
sulphuric acid was selected for testing the resistance of the clear
lacquers to sulphuric acid. The test coupons were placed on a heatable
plate and heated to 60.degree. C.
In the course of this procedure, it had to be ensured that the metal sheets
were lying flat, for the optimum transfer of temperature. At the end of
the heat-up phase, i.e. at 60.degree. C., one drop per minute was applied
to the surface of the clear lacquer. The total time was 30 minutes. After
the test period had elapsed the coating was washed with water. If
necessary, a brush could additionally be used for cleaning.
In order to assess the resistance to sulphuric acid, the period of
influence is quoted in minutes at which the first visible change in the
film (swelling), damage (matting) and attack of the base lacquer occurred.
______________________________________
Comparison
Examples according to the invention
2 from EPA-0
Example 5 6
653 468
______________________________________
20.degree. 92 93 88
(DIN 67530)
Pendulum 128 109 77
hardness:
(oscillations)
Sulphuric acid
test: 10% H.sub.2 SO.sub.4,
30'60.degree. C.
Swelling 19 18 17
Matting >30 27 22
Basecoat attack >30 >30 30
Condensation intact surface intact surface matting
chamber (DIN
50017) after 240
hours:
______________________________________
Top